Polycystic ovary syndrome (PCOS) affects 20–33% of women of reproductive age and the leading cause of infertility. Treatment includes lifestyle modification, metformin, ovulation induction, surgery, in vitro fertilization. Clomiphene citrate is most commonly used for ovulation induction but is antiestrogenic. Clomiphene resistance occurs in 15–20% of patients. Letrozole, an aromatase inhibitor, inhibits aromatization thus conversion of androstenedione and testosterone to estrogen in the ovary. This releases the hypothalamic/pituitary axis from estrogenic negative feedback, follicle stimulating hormone secretion increases, stimulating ovarian follicular development.
We compared clomiphene citrate vs letrozole for ovulation induction in the treatment of anovulatory infertility in women with the polycystic ovarian syndrome. Two hundred consecutive women were observed for a number of cycles required to achieve ovulation, follicular growth, endometrial thickness, dominant follicle size, pregnancy, multiple, and abortion rates. The groups were matched for age, parity, duration of married life, menstrual regularity and prior history of treatment for infertility.
Clomiphene showed a significantly increased number of follicles. Monofollicular development and endometrial thickness were higher in the letrozole group. The difference in dominant follicle size, number of cycles to achieve pregnancy or difference in ovulation rate per cycle, number of pregnancies and pregnancy losses per cycle lacked statistical significance. Greater number of follicles in the clomiphene group did not result in increased pregnancy rate. A number of pregnancies were marginally higher but not statistically significant in the letrozole group. There were one quadruplet and one twin gestation in the clomiphene group with none in the letrozole group. This data was not sufficient for statistical analysis. There were no instances of ovarian hyperstimulation syndrome or congenital anomalies in either group.
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